This invention relates generally to a method and apparatus utilized in hydrocarbon exploration. More specifically, the invention relates to the utilization of acoustic sources and receivers to determine acoustic properties of geologic formations as a logging tool traverses them, be it a wireline logging tool or a logging while drilling tool. More particularly, the present invention is directed to methods of and apparatus for determining certain acoustic velocities characteristic of the pertinent geologic formations.
Geologists and geophysicists are interested in the characteristics of the formations encountered by a drill bit as it is drilling a well for the production of hydrocarbons from the earth. Such information is usefull in determining the correctness of the geophysical data used to choose the drilling location and in choosing subsequent drilling locations. In horizontal drilling, such information can be useful in determining the location of the drill bit and the direction that drilling should follow.
Such information can be derived in a number of ways. For example, cuttings from the mud returned from the drill bit location can be analyzed or a core can be bored along the entire length of the borehole. Alternatively, the drill bit can be withdrawn from the borehole and a xe2x80x9cwireline logging toolxe2x80x9d can be lowered into the borehole to take measurements. In still another approach, called xe2x80x9cmeasurement while drillingxe2x80x9d (xe2x80x9cMWDxe2x80x9d) or xe2x80x9clogging while drillingxe2x80x9d (xe2x80x9cLWDxe2x80x9d) tools make measurements in the borehole while the drill bit is working. There are a wide variety of logging tools, including resistivity tools, density tools, sonic or acoustic tools, and imaging tools.
An acoustic logging tool collects acoustic data regarding underground formations. The purpose of such a tool is to measure the xe2x80x9cinterval transit timexe2x80x9d or the amount of time required for acoustic energy to travel a unit distance in a formation. In simple terms, this is accomplished by transmitting acoustic energy into the formation at one location and measuring the time that it takes for the acoustic energy to travel to a second location or past several locations. The measurement is complicated by the fact that the tool is roughly in the middle of a borehole of unknown diameter and is surrounded by mud. Further, the formation along the borehole may have been disturbed by the action of the drill bit and may no longer have the same acoustic characteristics as the undisturbed formation.
In general, in one aspect, the invention features a logging-while-drilling acoustic logging tool comprising one or more acoustic transmitters and one or more acoustic receivers. One or more elements of a set comprising the acoustic receivers and the acoustic transmitters are spaced radially apart from one or more of the remaining elements of the set.
Implementations of the invention may include one or more of the following. The tool may include a transmit module coupled to the acoustic transmitters, a data acquisition module coupled to the acoustic receivers, and a transmitter trigger signal coupled to the transmit module and to the data acquisition module. The transmit module may be configured to initiate transmission via the acoustic transmitters and the data acquisition module may be configured to initiate data acquisition via the acoustic receivers.
In general, in another aspect, the invention features a logging-while-drilling acoustic logging tool comprising a multipole-capable acoustic source.
Implementations of the invention may include one or more of the following. The multipole-capable acoustic source may comprise one or more acoustic transmitters.
In general, in another aspect, the invention features an acoustic logging tool comprising a multipole capable acoustic source. The source comprises one or more acoustic transmitters. Each acoustic transmitter is configured to have a transmission direction. An acoustic transmitter is paired with another acoustic transmitter having an azimuthally opposite transmission direction.
Implementations of the invention include one or more of the following. The acoustic logging tool may comprise a transmitter module coupled to the acoustic transmitters. The transmitter module may be configured to fire the acoustic transmitters. The transmitter module may be configured to fire each acoustic transmitter. One or more of the acoustic transmitters may be configured to transmit acoustic energy at one or more selectable frequencies. The transmitter module may be configured to control frequency content of the acoustic energy transmitted by one or more acoustic transmitters. The transmitter module may be configured to control timing of the acoustic energy transmitted by one or more acoustic transmitters. The transmitter module may be configured to cause one of the acoustic transmitters to transmit acoustic energy and at least one other acoustic transmitter to transmit acoustic energy with a controlled time delay or phase shift relative to the one acoustic transmitter. The transmitter module may be configured to control magnitude of the acoustic energy transmitted by one or more acoustic transmitters.
In general, in another aspect, the invention features a logging-while-drilling acoustic logging tool comprising a multipole-capable acoustic receiver. The logging-while-drilling acoustic logging tool may further comprise a multipole-capable acoustic source.
In general, in another aspect, the invention features an acoustic logging tool comprising a multipole capable acoustic receiver, the receiver comprising one or more acoustic receivers. Each acoustic receiver is configured to have a receive direction. An acoustic receiver is paired with another acoustic receiver having an azimuthally different receive direction.
Implementations of the invention include one or more of the following. The acoustic logging tool may comprise one or more sample-and-hold amplifiers, each sample-and-hold amplifier configured to sample and hold a signal originating in the acoustic receivers and conditioned by one or more conditioning components. The one or more sample-and-hold amplifiers may sample substantially simultaneously. The acoustic logging tool may comprise a processor. The conditioning components may comprise an adjustable high-pass filter having a cutoff frequency adjustable under control of the processor. The processor control of the cutoff frequency may be adaptive. The conditioning components may comprise an adjustable amplifier having a gain adjustable under control of the processor. The adjustable amplifier may be configured to be adjusted separately for one or more receiver channels. The processor control of the adjustable amplifier may be adaptive. The conditioning components may comprise a low pass filter. The conditioning components may comprise a pre-amplifier interfaced to the receivers. The conditioning components may comprise an amplifier. The acoustic logging tool may comprise an analog-to-digital converter for converting the analog signals held by the one or more sample-and-holds to a digital signal. The digital signal may be coupled to the processor. The acoustic logging tool may comprise a multiplexer for selecting, based on an address, one of the analog signals held by the one or more sample-and-holds to couple to the analog-to-digital converter. The acoustic logging tool may comprise a counter for producing the address and a clock. The clock may drive the counter and the analog-to-digital converter. The counter may have a sample-and-hold output configured to cause the sample-and-holds to sample. The counter may have a processor output configured to inform the processor that the counter had completed a counter cycle. The acoustic logging tool may comprise a multipole-capable acoustic source. The acoustic logging tool may comprise one or more analog to digital converters, each analog to digital converter configured to sample a signal originating in one of the acoustic receivers and conditioned by one or more conditioning components. The one or more analog to digital converters may sample substantially simultaneously.
The acoustic logging tool may comprise one or more multiplexers and one or more analog to digital converters. Each analog to digital converter may be configured to sample signals originating in the acoustic receivers, conditioned by one or more conditioning components and multiplexed by one or more multiplexers.
In general, in another aspect, the invention features a logging-while-drilling acoustic logging tool comprising a tool housing, a first acoustic transmitter configured to transmit acoustic energy generally in a first direction relative to the tool housing, a second acoustic transmitter configured to transmit acoustic energy generally in a second direction relative to the tool housing, a processor configured to make acoustic measurements in the first direction using any combination of transmitters and a receiver. The processor is further configured to make acoustic measurements in the second direction using any combination of transmitters and receiver.
In general, in another aspect, the invention features a logging-while-drilling tool for measuring acoustic velocity in any geologic formation comprising an acoustic transmitter configured to create and sustain multiple types of acoustic waves in the geologic formation.
In general, in another aspect, the invention features an acoustic logging tool comprising a transmit module configured to cause one or more acoustic transmitters to transmit acoustic energy. The tool includes a data acquisition module configured to accept signals from one or more acoustic receivers, convert the signals to unprocessed data, and process the unprocessed data to produce processed data. The tool includes a data storage module configured to store the processed data.
Implementations of the invention may include one or more of the following. The data storage module may be configured to store the unprocessed data. The data storage module may be configured to store processed and unprocessed data. The data storage module may be configured to store processed and unprocessed data for an entire mission.
The data storage module may be configured to compress the processed data. The data storage module may adaptively choose a compression algorithm to compress the processed data. The data storage module may be configured to apply error correction code to the processed data before storage. The data storage module may adaptively choose an error correction coding algorithm to apply error correction code to the processed data before storage.
In general, in another aspect, the invention features a logging-while-drilling acoustic logging tool comprising a processor, and a computer-readable medium coupled to the processor having computer-readable program code embodied thereon for controlling the operation of the logging-while-drilling acoustic tool. The tool comprises two or more radially offset transmitters.
Implementations of the invention may include one or more of the following. The computer-readable program code may comprise computer-readable code for causing the processor to compute one or more formation acoustic velocities using the collected data. The computer -readable program code may include computer-readable code for causing the processor to store the computed one or more acoustic velocities in the data memory. The computer-readable program code may include computer-readable code for causing the processor to provide the collected data to a communication device configured to transmit the collected data. The computer-readable program code may comprise computer-readable code for causing the processor to provide the computed one or more acoustic velocities to a communication device configured to transmit the computed velocity.
In general, in another aspect, the invention features a method for acoustic logging-while-drilling using an acoustic logging tool comprising a processor, one or more transmitters under processor control and one or more receivers under processor control, the method comprising spacing one or more elements of a set comprising the transmitters and the receivers radially apart from one or more of the remaining elements of the set, firing the one or more transmitters, and collecting data from the receivers.
Implementations of the invention may include one or more of the following. The method may include computing one or more formation velocities from the collected data. The method may include storing the computed one or more formation velocities. The method may include storing the collected data.
In general, in another aspect, the invention features a method for acoustic logging using an acoustic logging tool comprising a processor, a transmitter under processor control and a receiver under processor control, the method being accomplished by the processor. The method comprises transmitting acoustic energy into a formation using the transmitter, controlling the azimuthal profile of the acoustic wave emitted into the formation, and receiving acoustic energy from the formation using the receiver.
Implementations of the invention may include one or more of the following. The method may comprise processing the received acoustic energy using the processor to produce processed data. The method may comprise adaptively processing the received acoustic energy using the processor to produce processed data. Adaptively processing may comprise applying decision logic to determine which of one or more acoustic signal processing algorithms to execute. The method may comprise compressing the processed data. Compressing may comprise adaptively compressing the processed data. The method may comprise error correction coding the processed data. Error correction coding may comprise adaptively error correction coding the processed data.
In general, in another aspect, the invention features a logging-while-drilling acoustic logging tool comprising a tool housing, a first acoustic receiver configured to receive acoustic energy generally from the first direction relative to the tool housing, and a second acoustic receiver configured to receive acoustic energy generally from the second direction relative to the tool housing. A processor is configured to make acoustic measurements in the first direction using any combination of a transmitter and receivers. The processor is further configured to make acoustic measurements in the second direction using any combination of transmitter and receivers.
In general, in another aspect, the invention features a logging-while-drilling acoustic logging tool comprising a processor, a computer-readable medium coupled to the processor having computer-readable program code embodied thereon for controlling the operation of the logging-while-drilling acoustic tool; and two or more radially offset receivers.
Implementations of the invention may include one or more of the following. The computer-readable program code may comprise computer-readable code for causing the processor to compute one or more formation acoustic velocities using the collected data. The computer-readable program code may comprise computer-readable code for causing the processor to store the computed one or more acoustic velocities in the data memory. The computer-readable program code may comprise computer-readable code for causing the processor to provide the collected data to a communication device configured to transmit the collected data. The computer-readable program code may comprise computer-readable code for causing the processor to provide the computed one or more acoustic velocities to a communication device configured to transmit the computed velocity.